Occurrence of Phytophthora Rot of Strawberry Caused by Phytophthora nicotianae var. nicotianae

A severe Phytophthora rot of strawberry caused by a species of Phytophthora has been widely occurred at major cultivation areas of Kimhae on August in 1997. Incidence of the disease was obtained in the range of 69.2~83.6% in surveyed 4 fields and showed an average of 75.2%. A species of Phytophthora was mostly isolated from the crown of infected strawberry plants and all the isolates were identified as P. nicotianae var. nicotianae (=P. parasitica). The fungus showed strong pathogenicity on strawberry by inoculation test. As a result of the leaf inoculation using mycelial disks of the fungus, both leaves and petioles were darkly browned, and were finally blighted As a result of the root inoculation of zoospore suspension, both roots and crowns were rotten with dark brown. Although the fungus produced sporangia either on V-8 juice agar medium or liquid medium, the sporangia observed on the liquid medium appeared to be broadly turbinate and noncaducous. Moreover the fungus cultured on the liquid medium often produced sporangia having two papilla. The number of zoospores in sporangia was found to be ranged from 3 or 4 to as many as 20 or 25. In addition, the released zoospore from the sporangium became the cystospore during the prolonged culture of the fungus.